Bicycle exercise is well known to be health-beneficial exercise in operation of both transportation- and gym-purposed bicycles. Conventional bicycles are operatably driven by force exerted on pedals thereof. Nevertheless, the present inventor has found that, bicycles actuated by body motion, are also of great significance in concern of body health and exercise, as comparable to the conventional leg-driven bicycles. Therefore, the present invention is here to provide a novel type of bicycles operatably urged by body motion.